Conventional toners for electrostatic latent image developing are typically manufactured using kneading and classifying methods by fusion-kneading a toner structural component, such as colorant and the like, in a binder resin, followed by cooling and solidifying the kneaded material, and then subsequently pulverizing and classifying said material. Pressure fixing methods, flash fixing methods, oven fixing methods and similar non-contact heat-fixing methods, heating roller fixing methods and similar contact heat-fixing methods are conventionally used as toner fixing methods in image forming apparatuses, such as electrophotographic apparatuses. In particular, contact heat-fixing methods are the most widely used fixing methods because they are capable of high speed fixing compared to pressure fixing methods, have a high thermal efficiency compared to non-contact heat fixing methods, are capable using a relatively low temperature heat source, and can be employed in compact and energy efficient devices.
In recent years, electrophotographic apparatuses using contact-type heat fixing methods have required ever more high-speed and energy efficient operation. If low temperature fixing is realized, not only is the electrophotographic apparatus more energy efficient, warm up time can also be reduced so as to provide optimal operational characteristics. In such contact-type heat fixing methods, for example, a disadvantage arises in that a so-called offset phenomenon may occur during fixing of a toner image via heating roller fixing methods when a portion of the toner comprising an image adheres to the surface of said heating roller and is subsequently transferred back to a transfer sheet transported thereto. As a result, the image becomes undesirably soiled. Japanese Laid-Open Patent Application No. 49-65231 discloses preventing the offset phenomenon by adding, for example, polypropylene wax as an anti-offset agent (i.e., separation agent).
In recent years, copiers provided with auto document feeders and duplex copying devices have become standard in conjunction with multifunctionality and higher speed electrophotographic copying speeds. Problems such as bleeding and soiling of an image, however, often arise in such apparatuses when the surface of the copy image is rubbed by a roller during document transport, or sheet transport during the second copying process of second-side copying, and multi-color copying. Other similar image quality problems occur when transfer sheets designated for multiple copy overlays are temporarily held within the apparatus and subsequently fed one sheet at a time by a feed roller to receive the second copy. Toners that are subject to the aforesaid disadvantages are said to have poor smearing characteristics. To improve smear characteristics, it has been disclosed that polyethylene wax may be added during the kneading process (e.g., Japanese Laid-Open Patent Application No. 4-313762).
However, when polypropylene wax and polyethylene wax are simultaneously added during the kneading process of the above-mentioned kneading-pulverization methods to improve simultaneously the offset characteristics and smear characteristics of a toner, other problems or disadvantages occur. For instance, filming may occur during copying, thereby reducing toner flow characteristics and chargeability. By using polypropylene wax and polyethylene wax together, the compatibility of said materials with the binder resin becomes adversely affected. For instance, waxes, and particularly polyethylene wax is freed, resulting in said free wax adhering to the photosensitive member and causing filming of said member, thereby adversely affecting toner flow characteristics and chargeability.
Accordingly there remains a need for better and reliable toners, and methods for making toners that address the above problems and disadvantages and that provide a toner having, for example, desirable smearing, offset, filming, flow and chargeability characteristics.